A nuclear fuel assembly for a pressurized water reactor (PWR) traditionally comprises a bundle of nuclear fuel rods and an armature, the armature comprising a bottom nozzle, an upper nozzle, guide tubes connecting the bottom nozzle to the upper nozzle, and retention grids attached on the guide tubes. The rods extend between the bottom nozzle and the upper nozzle, and through the grids that retain them on the armature.
In operation, the assembly is positioned in a nuclear reactor such that the rods extend vertically, and water flows at a high speed along the rods of the nuclear fuel assemblies, passing through the bottom nozzle and the upper nozzle. The water serves as coolant for the heat exchanges, and moderator for the nuclear reaction.
There is a risk of the debris transported by the water damaging the rods of the fuel assembly and requiring that the reactor be stopped to change a rod or an entire assembly. Yet the assemblies are costly, and stopping the reactor is expensive for the operator. To limit this risk, the bottom nozzle has, inter alia, the function of filtering the debris to prevent it from passing through the bottom nozzle.
Nevertheless, a risk remains that debris may infiltrate between two bottom nozzles of two assemblies positioned side by side in the reactor.
JP 6003470 describes a bottom nozzle of the aforementioned type, comprising an anti-debris element positioned on a lateral face of the nozzle, the anti-debris element being made of a shape memory alloy such that the anti-debris element protrudes from the lateral face from a temperature close to the operating temperature of the reactor (indicated as being 300° C.) to filter the debris, and does not protrude from the lateral face below that operating temperature to facilitate the insertion or removal of the assembly into or out of the core of the reactor, respectively.